fix($shared-utils): improve title inference and header extraction for markdown links syntax

[nuochong]

Summary

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• Other, please describe:

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before

after

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

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• Chrome
• Firefox
• Safari
• Edge
• IE

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature
• Related documents have been updated
• Related tests have been updated

To avoid wasting your time, it's best to open a feature request issue first and wait for approval before working on it.

Other information:

[billyyyyy3320]

Please at least provide summary or the issue you were facing

[nuochong]

The following title cannot be resolved properly

### [Subscript](https://github.com/markdown-it/markdown-it-sub) / [Superscript](https://github.com/markdown-it/markdown-it-sup)
### [\<ins>](https://github.com/markdown-it/markdown-it-ins)
### [\<mark>](https://github.com/markdown-it/markdown-it-mark)

It was wrongly parsed as

<span>Subscript](https://github.com/markdown-it/markdown-it-sub) / [Superscript</span>
<span>\</span>
<span>\</span>

The correct analysis should be

<span>Subscript / Superscript</span>
<span><ins></span>
<span><mark></span>

Sample snippet from: https://markdown-it.github.io/

@billyyyyy3320

[billyyyyy3320]

Thanks @nuochong!

There're unit tests for both files, could you update test cases?

[nuochong]

sure